Before we start to forget what happened at the election, we ought to reflect on the most gobsmacking aspect of the result. I do not mean that the Tories won. I mean how they won. Some have attributed their shock majority to the dark arts of Lynton Crosby. Others to the lack of appeal of Ed Miliband. Some opine that the Tory win demonstrates that the English are an essentially conservative people. Others think Labour’s failure is a symptom of a worldwide crisis in social democracy. On they go, the theories. I have barely touched on the many interesting explanations for what happened. And they are all wrong. For sure, they may be among the factors that contributed to what happened on 7 May, but they are all insignificant compared with the main explanation for why David Cameron is at Number 10 enthroned atop a Conservative parliamentary majority.

There is a big, basic and brute reason why we have just heard a Tory Queen’s speech, will soon be listening to a Tory budget and have five years or so of Tory law-making ahead of us. It is so bloody obvious that no one is talking about it – it is the electoral system.

By no normal definition of the word popular were the Conservatives popular at the election. They received 36.9% of the vote. By no normal definition of the word mandate did they get the endorsement of the electorate to fully implement their manifesto. Nearly two-thirds of voters did not put their cross in the Tory box. Factor in the turn-out and the Conservatives secured the backing of less than a quarter of the registered electorate. It is first past the post that alchemises a minority vote share into more than half of the seats in the House of Commons, every seat in the cabinet and the power to pursue an entirely Tory agenda for the next five years.

The other party greatly favoured by winner takes all were the Scottish Nationalists. Their hugely swollen contingent of MPs have announced their arrival at Westminster in noisy fashion. When not winding up Tory traditionalists by clapping in the chamber, they are battling with Labour for buttock space on the opposition benches. More seriously, the size of Nicola Sturgeon’s clan, now the third largest group in the Commons, will entitle them to lots of significant perks in the party pecking order. They will secure more debate days. They will have many more places on select committees, including some chairmanships. Their leader in the Commons, Angus Robertson, will get two guaranteed pops at David Cameron every prime minister’s questions. They will maximise the advantages of that position to claim that they alone speak for Scotland at Westminster. As you would, if you were them. It is first past the post that has awarded them all these privileges. Half of Scotland’s voters wanted to be represented by the SNP. They have now got 56 of its 59 MPs to give megaphonic expression to their views; 50% of Scots did not want to send a Nationalist MP to Westminster. That half of the nation is represented by just three MPs, one each for Labour, the Tories and the Lib Dems, which may go down to just two if Alistair Carmichael is unseated by a recall byelection.

Compare and contrast the jubilantly numerous Nationalists now swarming around the Palace of Westminster with the miserable fate of the shrivelled band of Lib Dems. They received about a million more votes than the SNP, but while the Nationalists celebrate, the Lib Dems are wearing mourning weed. All their big names defenestrated bar Nick Clegg and just seven other MPs huddling together for warmth. This has prompted some to recommend that they might as well wind up as a party and find something more rewarding to do with their lives. That suggestion is unfair not just to the important liberal tradition in British politics, but also to the 2,415,862 people who voted for the Lib Dems on 7 May. They must have thought there was a continuing purpose for the party. If seats were allocated in proportion to votes, they would have a respectable 51 MPs to represent them and no one would be telling the Lib Dems to shut up shop.

For the electoral system has more than one distorting effect. Having turned votes into seats in a wildly disproportionate way, it then reinforces that by skewing the shape of political argument in the years afterwards. During the coalition period, producers of TV and radio discussion programmes would want to have a Lib Dem on the panel just about every week. In the years to come, I suspect sightings of Lib Dems on programmes such as Question Time will be much rarer and there will be a lot more MPs from the SNP sitting around David Dimbleby’s table. The Lib Dems beat the SNP in votes, but because of the relative weight of their MPs, there will be much more amplification of nationalist views in the media than there will be of liberal views.

The Greens were another victim. They quadrupled their support to a million plus, but still have just the one MP – Caroline Lucas – to speak for them in parliament. Compare that with Northern Ireland’s Democratic Unionists, who may become important players when David Cameron’s majority is eroded by byelection losses. The DUP, like the SNP, are a beneficiary of the way in which first past the post rewards parties whose support is geographically concentrated. The Democratic Unionists received fewer than 190,000 votes, yet that yielded them eight MPs.

The people worst treated by the electoral system were those who voted for Ukip. There were approaching 4 million of them, making them third in share. For all those votes, they were rewarded with just the one MP, Douglas Carswell. He’s an interesting chap with some distinctive positions that are not, I suspect, wholly representative of the views of all Ukip voters. To them, this must seem not just grossly unfair, but utterly undemocratic. This has to be bad for the reputation of Westminster among those already most alienated from it. If you were a Ukip voter, you probably went into a polling station already thinking that politics is a rotten establishment racket. Now you must be absolutely sure it is.

The flaws of first past the post, especially when used in a multi-party political climate for which it was never designed, are well known. What’s special about this election is just how stark they have become. The Electoral Reform Society will tomorrow publish a study that marshals the evidence to argue that this was the most disproportionate result in British election history. It also makes a compelling case that the electoral system is now working to cleave an already fractious kingdom by artificially exaggerating our regional and national divides. Look at one of those maps with constituencies coloured to show the party of the MP. The sea of blue in the home counties leads you to think that there are virtually no Labour voters there when, in fact, there are quite a lot. The sea of red in the big cities of the north suggests that there are no Tory voters there when, in fact, there are quite a lot. Looking at the map you’d think there was barely anyone who wasn’t a Nationalist voter north of the Tweed when, in fact, half of Scotland voted for a unionist party. These many millions of voters have been cheated out of representation.

To an outside eye, this looks both absurd and outrageous. I was recently in conversation with some European diplomats. All of their countries used some form of more proportional voting. They expressed amazement that we still turn votes into power in a way that is so self-evidently unfair and some surprise that there was not a great popular outcry about it.

One reason that electoral reform has not gained enough traction in this country to force change is that the two biggest parties have never seen it to be in their interests to embrace the cause. This might begin to alter in the case of the Labour party. They now have to contemplate another five years in opposition, half a decade in which to reflect on their failure to do anything about first past the post when they were in government or to help the Lib Dems pursue reform in the last parliament. Labour is going to pay for it – literally so. The Tories intend to use the majority gifted to them by the electoral system to further entrench their advantage when it comes to money by making it harder for the trade unions to raise funds for Labour.

Some people do get cross about it. Shortly after the election, a petition was organised and 478,000 names signed the call for electoral reform. It was delivered to Number 10. Unfortunately for reformers, that is the one address in the UK least likely to be interested in changing the way we elect governments. David Cameron is the last person who is going to be interested in reforming a voting system that has just converted a minority of the vote into all the spoils of power. When he looks at first past the post, far from seeing a broken system, he sees one that has just worked perfectly for him.